Re: [RFC PATCH v8 21/21] riscv: Turn has_vector into a static key if VECTOR=y

From: Greentime Hu <greentime.hu@sifive.com>
To: Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
Cc: linux-riscv <linux-riscv@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Vincent Chen <vincent.chen@sifive.com>
Subject: Re: [RFC PATCH v8 21/21] riscv: Turn has_vector into a static key if VECTOR=y
Date: Mon, 4 Oct 2021 23:04:11 +0800	[thread overview]
Message-ID: <CAHCEehKGTA0ygyf4KNVovc5nAo_UZUus7QBQLeJHt1Py3Xb-mw@mail.gmail.com> (raw)
In-Reply-To: <20210915222456.1de541df@xhacker>

Jisheng Zhang <jszhang3@mail.ustc.edu.cn> 於 2021年9月15日 週三 下午10:31寫道：
>
> On Thu,  9 Sep 2021 01:45:33 +0800
> Greentime Hu <greentime.hu@sifive.com> wrote:
>
> > Just like fpu, we can use static key for has_vector.
> > The has_vector check sits at hot code path: switch_to(). Currently,
> > has_vector is a bool variable if VECTOR=y, switch_to() checks it each time,
> > we can optimize out this check by turning the has_vector into a static key.
> >
>
> has_vector is newly introduced in this patch set so I believe this patch can
> be folded into has_vector introducing patch, I.E patch 6
>
ok, I'll split this patch and merge these codes into its related patches.

>
> > Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
> > ---
> >  arch/riscv/include/asm/switch_to.h     | 10 +++++++---
> >  arch/riscv/kernel/cpufeature.c         |  4 ++--
> >  arch/riscv/kernel/kernel_mode_vector.c |  4 ++--
> >  arch/riscv/kernel/process.c            |  8 ++++----
> >  arch/riscv/kernel/signal.c             |  6 +++---
> >  5 files changed, 18 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> > index b48c9c974564..576204217e0f 100644
> > --- a/arch/riscv/include/asm/switch_to.h
> > +++ b/arch/riscv/include/asm/switch_to.h
> > @@ -71,7 +71,11 @@ static __always_inline bool has_fpu(void) { return false; }
> >  #endif
> >
> >  #ifdef CONFIG_VECTOR
> > -extern bool has_vector;
> > +extern struct static_key_false cpu_hwcap_vector;
> > +static __always_inline bool has_vector(void)
> > +{
> > +     return static_branch_likely(&cpu_hwcap_vector);
> > +}
> >  extern unsigned long riscv_vsize;
> >  extern void __vstate_save(struct __riscv_v_state *save_to, void *datap);
> >  extern void __vstate_restore(struct __riscv_v_state *restore_from, void *datap);
> > @@ -120,7 +124,7 @@ static inline void __switch_to_vector(struct task_struct *prev,
> >  }
> >
> >  #else
> > -#define has_vector false
> > +static __always_inline bool has_vector(void) { return false; }
> >  #define riscv_vsize (0)
> >  #define vstate_save(task, regs) do { } while (0)
> >  #define vstate_restore(task, regs) do { } while (0)
> > @@ -136,7 +140,7 @@ do {                                                      \
> >       struct task_struct *__next = (next);            \
> >       if (has_fpu())                                  \
> >               __switch_to_fpu(__prev, __next);        \
> > -     if (has_vector)                                 \
> > +     if (has_vector())                                       \
> >               __switch_to_vector(__prev, __next);     \
> >       ((last) = __switch_to(__prev, __next));         \
> >  } while (0)
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index af984f875f60..0139ec20adce 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -23,7 +23,7 @@ __ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
> >  #endif
> >  #ifdef CONFIG_VECTOR
> >  #include <asm/vector.h>
> > -bool has_vector __read_mostly;
> > +__ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_vector);
> >  unsigned long riscv_vsize __read_mostly;
> >  #endif
> >
> > @@ -157,7 +157,7 @@ void __init riscv_fill_hwcap(void)
> >
> >  #ifdef CONFIG_VECTOR
> >       if (elf_hwcap & COMPAT_HWCAP_ISA_V) {
> > -             has_vector = true;
> > +             static_branch_enable(&cpu_hwcap_vector);
> >               /* There are 32 vector registers with vlenb length. */
> >               rvv_enable();
> >               riscv_vsize = csr_read(CSR_VLENB) * 32;
> > diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
> > index 0d990bd8b8dd..0d08954c30af 100644
> > --- a/arch/riscv/kernel/kernel_mode_vector.c
> > +++ b/arch/riscv/kernel/kernel_mode_vector.c
> > @@ -110,7 +110,7 @@ static void vector_flush_cpu_state(void)
> >   */
> >  void kernel_rvv_begin(void)
> >  {
> > -     if (WARN_ON(!has_vector))
> > +     if (WARN_ON(!has_vector()))
> >               return;
> >
> >       WARN_ON(!may_use_vector());
> > @@ -140,7 +140,7 @@ EXPORT_SYMBOL(kernel_rvv_begin);
> >   */
> >  void kernel_rvv_end(void)
> >  {
> > -     if (WARN_ON(!has_vector))
> > +     if (WARN_ON(!has_vector()))
> >               return;
> >
> >       /* Invalidate vector regs */
> > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> > index 05ff5f934e7e..62540815ba1c 100644
> > --- a/arch/riscv/kernel/process.c
> > +++ b/arch/riscv/kernel/process.c
> > @@ -96,7 +96,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> >               fstate_restore(current, regs);
> >       }
> >
> > -     if (has_vector) {
> > +     if (has_vector()) {
> >               struct __riscv_v_state *vstate = &(current->thread.vstate);
> >
> >               /* Enable vector and allocate memory for vector registers. */
> > @@ -141,11 +141,11 @@ void flush_thread(void)
> >  int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> >  {
> >       fstate_save(src, task_pt_regs(src));
> > -     if (has_vector)
> > +     if (has_vector())
> >               /* To make sure every dirty vector context is saved. */
> >               vstate_save(src, task_pt_regs(src));
> >       *dst = *src;
> > -     if (has_vector) {
> > +     if (has_vector()) {
> >               /* Copy vector context to the forked task from parent. */
> >               if ((task_pt_regs(src)->status & SR_VS) != SR_VS_OFF) {
> >                       dst->thread.vstate.datap = kzalloc(riscv_vsize, GFP_KERNEL);
> > @@ -164,7 +164,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> >  void arch_release_task_struct(struct task_struct *tsk)
> >  {
> >       /* Free the vector context of datap. */
> > -     if (has_vector)
> > +     if (has_vector())
> >               kfree(tsk->thread.vstate.datap);
> >  }
> >
> > diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> > index d30a3b588156..6a19b4b7b206 100644
> > --- a/arch/riscv/kernel/signal.c
> > +++ b/arch/riscv/kernel/signal.c
> > @@ -192,7 +192,7 @@ static long restore_sigcontext(struct pt_regs *regs,
> >                               goto invalid;
> >                       goto done;
> >               case RVV_MAGIC:
> > -                     if (!has_vector)
> > +                     if (!has_vector())
> >                               goto invalid;
> >                       if (size != rvv_sc_size)
> >                               goto invalid;
> > @@ -221,7 +221,7 @@ static size_t cal_rt_frame_size(void)
> >
> >       frame_size = sizeof(*frame);
> >
> > -     if (has_vector)
> > +     if (has_vector())
> >               total_context_size += rvv_sc_size;
> >       /* Preserved a __riscv_ctx_hdr for END signal context header. */
> >       total_context_size += sizeof(struct __riscv_ctx_hdr);
> > @@ -288,7 +288,7 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
> >       if (has_fpu())
> >               err |= save_fp_state(regs, &sc->sc_fpregs);
> >       /* Save the vector state. */
> > -     if (has_vector)
> > +     if (has_vector())
> >               err |= save_v_state(regs, &sc_reserved_free_ptr);
> >
> >       /* Put END __riscv_ctx_hdr at the end. */
>
>